Heat sensitive sheets



p 2, 1964 w. R. LAWTON 3,149,992

HEAT SENSITIVE SHEETS Filed June 29, 1962 INDICATOR MATERIAL WHICH CHANGES COLOR BY REACTION WITH A BASIC ORGANIC AMINE SOLID CRYSTALLINE COMPLEX OF A HYDROXYPHENYL SUBSTITUTED CHROMAN AND AN AMINE ,\$UPPORT INVENTOR. WILLIAM R. LAWTO N BY Way, W M

ATTORNEYS United States Patent Office r Patented Sept. 22, 1964 3,149,992 HEAT SENSITIVE SHEETS William R. Lawton, Nashua, NH, assignor to Nashua Corporation, Nashua, N.H., a,corporation of Delaware Filed June 29, 1962, Ser. No. 206,186

8 Claims. (Cl. 117--36.9)

copying processes, in which a sheet is placed next to a graphic original and exposed to infrared radiation to cause selective heating of the dark areas of the original suflicient to form a copy thereof on the heat sensitive sheet. A more detailed description of this process is set forth in US. Patent No. 2,740,896. The sheets of this invention may also be used in recording devices in which marking is accomplished by means of a heated stylus. In addition this invention provides heat developable photographic sheets similar in characteristics to those described in the joint application of the present applicant and Eugene F. Lopez, Serial No. 808,012, filed April 22, 1959, now US. Patent No. 3,076,707.

The joint application Serial No. 808,012 describes heat sensitive sheets and compositions containing an indicator material which changes color in the presence of a basic organic amine in combination with a latent developer, which on heating yields an amine effective to give a color reaction. The latent developers employed in those sheets and compositions are the thermally dissociable crystalline molecular compounds consisting of an organic amine in combination with either urea thiourea or a bisphenol. Under normal storage conditions, they are solids which exhibit no substantial basic amine characteristics, and may therefore be intimately associated with the indicator material without causing a color reaction. i

The usefulness of the compositions heretofore developed has, however, been limited by the fact that the molecular compounds of urea, thiourea and the hisphenols are relatively unstable in the presence of moisture. They cannot therefore be applied to the sheet from aqueous systems, and the binder in which they are dispersed must be one that is soluble in an organic liquid in which the latent developer is not soluble. In addition, the sheets employing these complexes have a reducedshelflife when stored at high humidity.

The present invention is based on a continuation of the work described in the joint application and provides an improved heat marking sheet having improved stability in the presence of water, which may be coated with aqueous compositions. The invention further provides sheets of generally greater heat sensitivity which may be V marked or developed quicker and at lower temperatures.

This invention is based on the discovery that improved results may be attained when the latent developer for heat sensitive sheets and compositions is a crystalline adduct formed from a basic organic amine and a hydroxy- 1 phenyl substituted chroman. Adducts of 'this type are known to the art, see e.g., Cramer, Frederick E inschlussverbindungen'(Springer-Verlog, Berlin, 1954), and as a class they are generally useful when selected with reference to their physical characteristics as they relate to in the-presence of abasicorganic amine in combination with an; amine'adduct of a hydroxyphenyl substituted chroman. The indicator may be any of numerous wellknown materials which react with basic organic amines to give a color change, including the photosensitive azodye forming materials which provide photosensitive sheets capable of being developed merely by the application of heat.

Heat sensitive sheets are produced by providing a sheet of suitable backing material, such as paper, with a coating containing both the indicator material and crystals of the latent developer adduct in intimate potentially reactive association such that upon dissociation of the adduct, the amine is present throughout the coating. The adduct will generally be retained on the sheet by means of a resin binder, and the components may all be applied together in a single coat in which each is separately dispersed. Alternatively, the latent developer and indicator material may be applied in separate layers. In all cases it is contemplated that additional material such as pigments, antistatic and anti-friction ingredients may be incorporated in any of the coating compositions.

Because of the improved stability of the adducts of amines and hydroxyphenyl substituted chromans, they may be applied from aqueous solutions of binders, which may in turn be such water soluble polymers as glue, starch, polyvinyl alcohol, water soluble gums, carboxymethyl cellulose, hydroxyethylcellulose and the like. Not only are water based systems less expensive and generally safer to employ, but the use of water soluble resins themselves is preferable to the organic solvent soluble mate rials heretofore required, as they are less compatible with .the adduct, and therefore do not tend to interact with it.

It is seen that the greater stability of the systems of this invention results from the use of less compatible binders as well as from. the stability of the adducts in thepresence of moisture.

In selecting a particular latent developer for a given system, the adduct should be one that is stable under the conditions normally encountered in the manufacture, storage and shipment of materials of this type, which are -referredto in the specification and in the appended claims as normal and may be typified by conditions of temperature less than about 100 F. and a relative humidity less than 99 percent.

Theselection of suitable latent developers of the class 'herein set forth, may be readily made by one skilled in stability and dissociation temperature may be employed;

the investigations to date have largely'been centered about those chromansin which the hydroxyphenyl group is substituted in either'the 2 or 4 position. :Of the former, ,,the 2-hydroxy flavans, i.e., 2-(2'-hydroxyphenyl) chromans, are well known to the art and their amine complexes .have been found to'be generally useful as a class. Representative examples of this invention setting forth the best mode presently contemplated for carrying out the invention and representative types of latent developers'which may be used are given below.

The following Examples 1-6 inclusive describe'the preparation of representative adducts of amines and hydroxy- ;.phenyl substituted chromans: e

EXAMPLEI I Adducts of 7,4 '-DiethyLZ -HydrOxy-2,4,4-Trimethyl Flavan p m-Ethylphenol g.), dissolved in anhydrous acetone (43 g.) was saturated one hour with anhydrous I-lCl at C., kept at room temperature for two days, then warmed to 40 C. for six hours and stirred into an aqueous, two normal sodium hydroxide (500 cc.) solution to which 60 cc. diethyl ether was added. After two days at -20 C., the semi-solid product was collected in a Buchner funnel, dissolved in hexane, and treated with calcium chloride. After filtering, the dried hexane solution of 7,4'-diethyl-2'-hydroxy-2,4,4-trimethyl flavan was treated with grams cyclohexylamine and chilled for 2 4 hours at 20 C. The precipitate was collected and yielded 38 g. of the cyclohexylamine flavan complex as a fine, white microcrystalline product (M.P. 77-.7 9 C.).

EXAMPLE 2 Adducts of Cycl0hexanespir0-4-(2'-Hydr0xy-7,4'-Dimethyl-2,3-Tetramethylene) Flavan A mixture of m-cresol (400 g.) and cyclohexanone (240 g.) was'saturated with dry HCl for one hour at 0 C., kept for three days at room temperature and one day at 40-50 C., and was then stirred into 4 liters of an aqueous, 2 N sodium hydroxide solution. The product was extracted with a mixture of 1000 cc. diethylether and400 cc. hexane. The resulting solution was washed with water, dried over calcium chloride, and treated with charcoal, and was finally evaporated to dryness. The resinous cyclohexanespiro 4-(2-hydroxy-7,4-dimethyl- 2,3-tetramethylene) flavan was redissolved in hexane and 4 chilled and held at -.20 C. for four hours, and the solid amine complexes were then collected on a Buchner funnel and washed once with cold hexane. The following amines were complexed in this manner:

EXAMPLE 5 Adducts of 2'-Hydroxy-2,4,4,7,4'-Pentamethyl Flavan A mixture of m-cresol (440 g.) and acetone (260 g.) was saturated with gaseous HCl without cooling, and kept at 40 C. for two days with the exclusion of water. The resulting dark product was added to an excess of an aqueous 20 percent sodium hydroxide solution, a layer of ether poured on the surface, and the mixture was vigorously stirred causing the ether addition product of the dimeride to crystallize. After standing overnight ,in an open vessel, the solid was collected, washed separate aliquot portions were treated with benzylamine EXAMPLE 3 Adducts of 2-Hydroxy-2,4,4,6,7,4',5-Heptamethyl Flavan A solution of 3,4-dimethyl phenol (379 g.) in acetone (150 g.) was saturated at room temperature for one hour with anhydrous hydrogen chloride, after which it set to a red crystalline mass. After three days, the reaction mix- 'ture was crushed withan excess of dilute aqueous sodium hydroxide solution, washed, dried, and crystallized twice from isopropanol. The 2.'-hydroxy-2,4,4,6,7 ,4, ,5 '-heptamethylflavan had a M.P. of 161-1625, C, The diethanolamine complex was prepared by treating g. of

the flavan in a hexane-toluolfsolution with 10g. diethanolamine. Asolidproduct was obtained after chilling overnig ht at 2 0" CI The yield of the diethanolamine/flavan oomplexwas 3,2.i5 g-ff l d the, M.P."w as 1 53-,157[C. with considerable softening at much lower temperature.

EXAMPLE 4 I 2'-Hydroxyr2,4,4,6,5'-Pentamethyl Florian.

p-Cresol (648 g.) dissolved in acetone (232 g.) was cooled to 0 C. in an ice-salt bath and saturated for one hour with gaseous During this period, the'temperature rose to 15 C. The flask was sealed from atmospheric moisture, allowed to reach room temperature slowly and stood at room temperature for two days. "After {two days, the dark product was stirred into two liters of an" aqueous two i N sodium hydroxide solution during which timelthe mixture became colorless. nioxanemoo g) was added and, theimixture was stiri'edion the water *bath for thirty'minutes and left overnight at. -20 C.

The solid was collected and dried [over calcium chloride fun'der vacuum and recrystallized ffroni;600, cc, ofhexane with the addition of 20 gfdiioxan e togive the dioxane -hydroxy-2,4,4,6,5'-pentamethyl' flavan (M.P. 66-77 Twenty grams of the, flavan/hexane complex, and V a 1 0 grams amine were dissolved in 100, cc. of warm hexane,

thoroughly with water, dissolved in hexane, and dried over calcium chloride. To the filtered solution was added a little ether. The ether adduct separated in large colorless, thick rhombic prisms, M.P. 76-77 C. Complexes of the following amines were prepared by treating fifteen grams of the ether complex dissolved in 150 cc. hexane with 7 /2 g. of the amine chilling the mixture overnight and filtering oif the complex:

5.8diisopropylamine 83-87 E PLE 6 Adducts of Dianins Compound 4-p-Hydr0xyphenyl- 2,2,4-Trimethylchr0man A mixture of phenol (400 g.) and mesityl oxide g.) was saturated with gaseous I-ICl for eight hours while the flask was cooled in water. The reaction mixture was protected from atmospheric moisture and held at 40C. for four days, giving a brownish crystalline mass. One liter of boiling water was added and the mixture shaken vigorously and warmed on a water bath for one hour. The top aqueous layer was decanted and the lower layer again treated with boiling water and warmed on a water bath. The oily decanted layer was shaken with-250 ml. hot ethanol,"chilled'at -20 C. and the ethanol adduct separated 'on a. Buchner funnel and'washed' with cold ethanol. The product-was recrystallized fromethanol to give g. ethanol adduct of Dianins compound, M.P; -166 C. The comboiled fifteen minutes and treated wit-hflCO for thirty minutes. The resulting solid was boiled with water, collected, and dried over phosphoriq'anhydride under "vacuum (M.P. 156-157 C.); 'The' diethylamine/chro- 70 man' complex was prepared by mixing the resulting Dianins compound with diethylamine heating and then chilling' the mixture to give a product which was filtered "andwashe'd with cold hexane, M.P. 164-165f' C.r

preparinghea-t marking sheets iniaccordance with this invention, a sheet of :paper or other suitable web plex was dissolved in hot 2-normal sodium hydroxide,

Amine/chrornan adduct 20 Polyvinyl alcohol (Gelvatol 20/60) 2 Water 98 The mixture was milled in a ball mill for 24-48 hours and subsequently coated by means of No. 12 Mayer rod onto the paper based stock. In Examples 7 through 19 the amine/chroman adduct coating was applied to a 45 pound per ream (500 sheets, 24" x 30") Fitchburg direct process diazo paper stock to a dry coating weight of 3-5 pounds per ream. Upon drying, a coating containing the indicator material reactive with a base to give a color change, was applied over the amine/chroman adduct coating to a dry weight of 0.5-2 pounds per ream.

The following examples describe various formulations of indicator material suitable foruse in this invention.

EXAMPLE 7 A Conventional Diazo Composition Parts by weight The materials were added to the water in the order listed and mixed into solution for coating.

EXAMPLE 8 Ninhydrin Composition 7 Parts by weight Ninhydrin 6 Polyvinyl formal resin (Formvar 7/70) 8 Trichloroethylene 8 The resin binder was dissolved in the trichloroethylene 6 EXAMPLE 9 Hydrindantin Coating Composition Parts by weight Hydrindantin 129 Pliolite VT 49 VM & P naphtha 369 The ingredients were mixed together and ground for 24-48 hours in a ball mill.

EXAMPLE 10 Coating Composition Containing Phygon (2,3-Dichloronaphthoquinone) Parts by weight 2,3-dichloronaphthoquinone 1O Trichlorethylene 88.8

Polyvinyl butyral resin (Butvar B-76) 2.2

The materials were combined and ground for 24-48 hours in a ball mill.

EXAMPLE 11.

Coating Composition Containing Chloranil (Tetrachlorohydroquinone) Parts by weight Tetrachlorohydroquinone l0 Trichlorethylene 88.8

Polyvinyl butyral resin (Butvar B-76) 2.2

The materials were combined and ground for 24-48 hours in a ball mill.

In the following examples, typical pH indicators were employed, by dissolving the indicator in water or in a 50:50 methanol-water mixture at a concentration in the range of 0.52 percent.

Heat Sensitive Sheet Employed Commercial Diazo Paper In this example a commercial diazo paper, e.g., Ozalid No. 2088, Was overcoated with the dispersion of amine/ ehroman adduct.

In the following table, the various indicator materials (Examples 7-20) are set forth as column headings and the amine/chroman adducts (Examples 1-6) are line headings. Combinations which have been actually employed in the manner above are designated by an X in and the Ninhydrm is then added. the approprlate column and lme.

TABLE I Indicator Materials-Examples Amine/Chroman Adducts-Example 1 X X X 2. X X X X X 2. X X 3 X X 4. X X 4. X X 4. X X 4. X X 4. X X 4. X X 4. X X 5. X X X X 5. X X X X 5. X X 5. X X 5. X X X X 5. X X X 6. X X X 5. X X X X 6 X X X All of the sheets shown in Table I were suitable for copying on a Thermo-Fax copier. In addition, those described under Examples 7 and 20, employing diazo indicator systems, may be used as a conventional diazo sheet and exposed to ultra violet radiation through a graphic original, Following exposure, heating the sheet to cause dissociation of the amine/chroman adduct, causes the latent diazo image to be developed.

The accompanying drawing illustrates schematically a heat-sensitive sheet corresponding to this invention. The sheet is represented as being in cross-section.

Although the invention has been described above with specific reference to various preferred formulations, it is contemplated that obvious modifications will occur to those skilled in the art.

The indicator materials have been selected as representative of known materials which change color in the presence of a basic organic amine; they include diazo dye forming materials which are typically developed by amines, ninhydrin and quinone compounds which are frequently employed as color indicators for amines, and pH indicators which change color in the presence of the basic conditions provided by the amines. Other indicator materials than those described, which change color in the presence of a basic organic amine, and also the adducts of other hydroxyphenyl substituted chromans and other amines, will be known to the art, those specifically described being given as representative of these classes of materials. Other binders and coating techniques may also be employed, provided they result in the indicator material and the adduct being in intimate potentially reactive association, such that dissociation of the adduct will result in the desired colored change.

Modifications such as these obviously may be made without departing from the scope of this invention.

Havingthus disclosed my invention and described in detail preferred embodiments thereof, I claim and desire to secure by Letters Patent:

1. A heat marking copy sheet responsive to heating to an elevated activation temperature by changing visibly to a contrasting color comprising, in combination, a support carrying indicator material which changes color by chemical reaction with a basic organic amine; and a stable unreactive heat sensitive latent'developer in intimate association with said material for causing a color change upon heating said sheet to an activation temperature between 50 C. and 150 C., said developer being an organic amine in combination with a hydroxyphenyl substituted chroman forminga solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change.

2. The'c opy sheet defined by claim 1' wherein the indicator material is a" photosensitive azo dye forming material.

3. A heat marking copy sheet responsive to heating to anelevated activation temperature by changing visibly to 'a contrasting color comprising in combination a support carrying indicator material which changes color by chemical reaction with a basic organic amine, a stable unreactive heat sensitive latent developer in intimate association with said material for causing a color change upon heat ing said sheet to an activation temperature between 50 C. and C., and a binder for said developer, said developer being an organic amine in combination with a hydroxyphenyl substituted chroman forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change, and said binder being a water soluble resin.

4. The copy sheet defined by claim 3 wherein the indicator material is a photosensitive azo dye forming material.

5. A heat marking copy sheet responsive to heating to an elevated activation temperature by changing visibly to a contrasting color comprising, in combination, a support carrying a first layer which comprises indicator ma terial which changes color by chemical reaction with a basic organic amine; and a second layer which comprises a stable unreactive heat sensitive latent developer in intimate association with said material for causing a color change upon heating said sheet to an activation temperature between 50 C. and 150 C., said developer being an organic amine in combination with a hydroxyphenyl substituted chroman forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change.

The copy sheet defined by claim 5 where the indicator materialis an azo dye forming material.

7. A heat marking copy sheet responsive to heating to an elevated activation temperature by changing visibly to a contrasting color comprising, in combination, a support carrying a first layer which comprises indicator material which changes color by chemical reaction with a basic organic amine; and a second layer which comprises a stable unreactive heat sensitive latent developer in intimate association with said material for causing a color change upon heating said sheet to an activation temperature between 50T. C. and 150 C., and a binder for said developer, said developer being an organic amine in combination with a hydroxyphenyl substituted chroman forming a solid crystalline complex which is stable under normal conditions of temperature and humidity and dissociable at said activation temperature to yield said amine to cause said color change, said binder being a water solube resin.

8. The copy sheet defined by claim 7 wherein the indicator material is an azo dye forming material.

References Cited in the file of this patent UNITED STATES PATENTS Lawton et 211. Q. Feb. 5, 1963 

1. A HEAT MARKING COPY SHEET RESPONSIVE TO HEATING TO AN ELEVATED ACTIVATION TEMPERATURE BY CHANGING VISIBLY TO A CONTRASTING COLOR COMPRISING, IN COMBINATION, A SUPPORT CARRYING INDICATOR MATERIAL WHICH CHANGES COLOR BY CHEMICAL REACTION WITH A BASIC ORGANIC AMINE; AND A STABLE UNREACTIVE HEAT SENSITIVE LATENT DEVELOPER IN INTIMATE ASSOCIATION WITH SAID MATERIAL FOR CAUSING A COLOR CHANGE UPON HEATING SAID SHEET TO AN ACTIVATION TEMPERATURE BETWEEN 50*C. AND 150 C., SAID DEVELOPER BEING AN ORGANIC AMINE IN COMBINATION WITH A HYDROXYPHENYL SUBSTITUTED CHROMAN FORMING A SOLID CRYSTALLINE COMPLEX WHICH IS STABLE UNDER NORMAL CONDITIONS OF TEMPERATURE AND HUMIDITY AND DISSOCIABLE AT SAID ACTIVATION TEMPERATURE TO YIELD SAID AMINE TO CAUSE SAID COLOR CHANGE. 